Patent GB-684583-A (GB)
Title: Improvements in or relating to electric circuits comprising a cathode-ray tube
IPC: H03K29/00
Filed: 1950-07-26
Abstract: 684,583. Cathode-ray tubes. PHILIPS ELECTRICAL INDUSTRIES, Ltd. July 26, 1950 [July 29, 1949], No. 18665/50. Class 39(i) [Also in Groups XIX and XL(c)] A circuit comprising a cathode-ray tube having means for producing a cathode-ray beam and means for deflecting the beam, in which a collecting electrode system is coupled to a deflection electrode so that the beam is adapted to occupy any of a number of stable positions and means are provided for moving the beam from one stable position to a subsequent position and furthermore an auxiliary collecting electrode is provided which is connected to the deflection means for the beam, and is struck by the beam in an extreme position, said auxiliary collecting electrode having derived from it a pulse for moving the beam to an initial position, is characterized in that the said deflection electrode is coupled by way of a rectifier to an adjustable source of voltage. As shown the cathode-ray tube comprises means 2, 3, for producing the beam, deflection plates 4, 5, and collecting electrodes 6, 7, 12, the electrode 6 having a number of apertures such that the beam alternately strikes the electrode 6, and through an aperture of this electrode, the electrode 7. The current flowing to the electrode 7 then varies as a function of the deflection voltage at the electrode 5 as shown by curve 21. The relation between the current through the resistor 10 and the voltage at point 9 of the electrode 5 is shown by the straight resistance line 20. In the positions of equilibrium the current through the conductor 8 is equal to the current through the resistor 10, corresponding to intersections of the curves 20, 21, at the points 22 to 27, the intersections 28 to 32 providing positions of unstable equilibrium of the beam, since if the voltage at point 9 is assumed to be V2 the current through the conductor 8 exceeds the current through the resistor 10 and the natural capacitor C coupled to point 9 is discharged, the potential at point 9 thus decreasing and the beam moving to the stable position corresponding to the intersection 26. Similarly the beam will automatically move to this stable position if the voltage of the point 9 lies within the interval between voltages V3 and V4. The beam may be moved from a stable position to a subsequent position by applying a pulse to the point 9 such that the voltage at this point is abruptly varied to a value which lies within the attraction sphere of the subsequent stable position. Alternatively a pulse may be supplied to the deflection electrode 4. The beam originally occupies the initial position 22 and after five pulses reaches the position 27. The sixth pulse strikes an auxiliary electrode 12 and the resulting negative pulse is transferred through capacitor 13 to the deflection electrode 5. After a short time the capacitor C starts to discharge and the beam moves in the opposite direction, the electrode 12 discharging through the resistor 14 and providing a strong positive pulse which is transferred through the capacitor 13 to the deflection electrode 5 so that the voltage at point 9 is abruptly increased to a value higher than that of the voltage V5 and the beam moves to the initial position 22. The beam returns to the initial position after every six pulses, and in order to permit fly-back of the beam after an arbitrarily smaller number of pulses a diode 15 which may form part of the cathode-ray tube, prevents the potential at point 9 from exceeding the voltage V6 of the tapping point on the potentiometer 16. Specification 684,552, [Group XL(c)], is referred to.